23 footer with good rock ding evidence
I estimate that my rock guards take on 95%+ of any gravel tossed up to the trailer while in tow. I suspect that the percentage is higher, but lets leave 5% as a possibility and smaller rocks and grit hitting above the guards.
The road debris tossed up by OTHER VEHICLES, be it loose nuts, bolts, rock, glass, gophers, can be the real culprit in side window dings and breakage. We travel more non asphalt road than the majority of AS owners. We bought an extra pair of rock guards when in Jackson Center, OH some years back, so when we sell our trailer we can replace the originals that catch the brunt of gravel tossup.
Our drop down for the center window was star fractured by a stone tossed up by traffic either passing us or our passing them on the interstate. We also picked up a good ding of a stone on the curved aluminum, which would have easily cracked a window, if the 23 footer had curved side windows.
The gravel brush guards will reduce the amount of gravel dings on the tow frame, copper tubing underneath the AS and the aluminum bottom skin, but the killers are those rocks finding you by being on the road at the wrong time, rock tossed up in front of you, and hits your hood/windshield and gets deflected away or into your trailer.
My experience has been there are events that you cannot avoid. The bottom 36 inches are going to catch the brunt of the road gravel and a skirt behind the tow vehicle will reduce most of the dings to the "rock guards" but they still will bounce around under the AS and ding up the copper propane pipe and bottom of the AS. I took water pipe insulation hose, slipped it over the exposed copper pipes that are at a right angle to direction, used duct tape wrapping and now that takes the brunt of that damage. The puncture of your LP gas line would not be a happy event and avoiding that is a number one priority. Number two, the side glass panels... Unless some kind of plexiglass protection is made to cover those windows, which I think many AS owners with the side glass windows would purchase from an individual finding ones that can attach and be removed easily while parked... could make a killing. AS makes a killing selling the glass replacements... no incentive to prevent damage.
Look at a 23 foot AS, and smaller front end and count the rock dings at window level. That is the easiest way to estimate your chance of a broken window. When at the camp site, look behind your gravel guards and see if you have larger rock stuck between the rock guard and the AS aluminum skin. These are ones that are too large to drop out, as the rock guards are a perfect curved fit to the trailer, and will grind into your trailer skin. Also, check the Propane tanks and count the large "window crackers" that find their way into that area. You will be surprised at the amount of gravel you encounter... even on the interstate highways.
Good luck and I hope this helps someone.